Field of the Invention
The present invention relates to a sheet stacking apparatus, a control method of the sheet stacking apparatus, and a storage medium.
Description of the Related Art
Conventionally, there has been a sheet stacking apparatus that discharges a sheet to an elevatable sheet stacking unit. Such a sheet stacking apparatus prints an image on a sheet, and discharges the sheet having the printed image to the sheet stacking unit through a sheet discharge opening. As illustrated in FIG. 10A, the sheet stacking apparatus can stably stack sheets discharged through the sheet stacking opening, by causing the sheet stacking unit to descend according to an amount of sheets stacked on the sheet stacking unit. In this operation, the sheet stacking apparatus causes the sheet stacking unit to descend so as to bring an uppermost surface of the sheets stacked on the sheet stacking unit to a position near the sheet discharge opening.
As illustrated in FIG. 10B, when an obstacle that interrupts the descending of the sheet stacking unit is present under the sheet stacking unit, the sheet stacking unit hits against the obstacle while descending.
If the sheet stacking apparatus causes the sheet stacking unit to keep descending after hitting against the obstacle, a load is applied to a drive unit which is provided to lower the sheet stacking unit. This may cause damage to the sheet stacking unit and the drive unit.
Therefore, there is a known method of stopping a sheet discharge operation as well as a descending operation of a sheet stacking unit and then displaying a warning message, when the descending operation of the sheet stacking unit is interrupted by an obstacle (see Japanese Patent Application Laid-Open No. 2001-226022).
In the technique discussed in Japanese Patent Application Laid-Open No. 2001-226022, when noticing the displayed warning message, a user calls a serviceperson to lift the warning. The warning cannot be lifted until fixing of the sheet stacking apparatus is completed by the serviceperson.
The user needs to call a serviceperson and wait until maintenance is completed by the serviceperson, even though sheets can be stacked to the extent of not hitting against the obstacle.